If you are evaluating AI call transcription from any vendor, including AssemblyAI, you need to understand what the technology actually does, where it works well, and where it breaks. This article explains the mechanics of call transcription, shows you where to find answers on the vendor's own site, and tells you what a trial must prove before you commit budget.
This is an independent buyer's guide from Sysevo, and Sysevo is not affiliated with AssemblyAI. Current details about any vendor's capabilities, pricing, and compliance should be confirmed directly with that vendor.
What AI Call Transcription Actually Involves
Call transcription is not a single thing. It is a chain of separate problems, each with its own failure points. Audio arrives as a stream. The system converts it to text. It stores that text somewhere. And a human needs to find and read it weeks or months later. Break any link, and the whole system becomes useless, even if the transcription itself is 99% accurate.
The first problem is accuracy on messy audio. Most speech-to-text systems are trained on clean recordings: a single speaker, no background noise, studio microphone quality. Real calls are not that. A customer calls from their car. A sales rep is on a hands-free system in an open office. There is traffic, typing, office chatter. The transcription engine has to separate signal from noise, recognise accents that do not match its training data, and guess at industry jargon it has never seen before. A word misheard here produces a transcript that is useless for compliance, evidence, or training.
The second problem is speaker separation. On a two-party call, the system needs to know which words came from which person. This is called diarization. Get it wrong, and you cannot tell who promised what. A customer says "I want the blue model," the transcript attributes it to your staff member, and a dispute happens. Diarization fails reliably when one speaker is much quieter than the other, when there is crosstalk, or when the call quality is poor.
Accuracy Under Real Conditions and AI Call Transcription AssemblyAI
Transcription accuracy is measured in Word Error Rate (WER): the percentage of words the system gets wrong. Industry benchmarks put call transcription at 5-15% WER in clean conditions, and 20-40% WER with background noise or poor audio quality. That sounds precise. It is not. A 10% error rate might mean one mistake per sentence, distributed randomly. Or it might mean whole phrases are inverted. The same WER from two different systems can produce very different usability.
What matters for your business is whether the errors make the transcript useful. If you are capturing call notes for your CRM, a few mistakes per call might be fine. If you are using transcripts as a legal record or for compliance audit, they are not fine. A financial services firm using call transcription for regulatory recording cannot tolerate a 15% error rate, but a contractor using it to capture lead details can. When you evaluate any vendor, test on your own call audio, not on sample data. Record five real incoming calls, transcribe them, and read the output against the actual conversation. Count not just errors but errors that change meaning.
Accents and regional speech vary the error rate dramatically. If your customers or team members speak with an accent not well represented in the training data, error rates climb. English speakers from India, Scotland, or rural areas of the US typically see higher error rates than speakers from urban centres in the American South or Southeast England. When you run your trial, include calls from the accents your business actually deals with.
Speaker Separation and Storing Searchable Call Notes
Diarization is where many deployments fail in practice. The system correctly identifies that two people are speaking, but attributes the wrong words to each one. A call centre taking customer complaints needs to know which words came from the angry customer and which came from the agent. If the transcript scrambles that, it is worse than useless: it is misleading. Some transcription vendors publish diarization accuracy separately. Check whether the one you are evaluating does, and whether they test it on realistic call scenarios: multiple speakers, interruptions, overlapping speech.
Speaker separation on inbound customer calls is harder than on outbound sales calls. Inbound calls often have longer silences, uncertain turn-taking, and more emotional intensity. If you run outbound calling for lead qualification or appointment setting, diarization is simpler. If you manage inbound support or customer service calls, it is much harder. Tell any vendor exactly what your call pattern is, and ask for a trial with that audio type.
Where the transcript lives matters as much as what it says. Some transcription services store audio and text on their own servers indefinitely. Others delete it after 30 days, or let you download it once and then it is gone. Some let you search across hundreds of transcripts. Others require you to remember which call or date you need. If you are using transcription to train team members or to build a searchable record of customer feedback, storage and search are not optional. Check the vendor's data retention policy on their own documentation site. If it is not there in writing, ask in your initial call and request it in writing before you sign anything.
Where AI Call Transcription Struggles and When to Avoid It
Transcription is not a good fit for every business. If your calls are highly technical, involve specialized jargon specific to your industry, and the system has not been trained on that vocabulary, accuracy will be poor. A medical practice transcribing clinical notes, a law firm recording client consultations, or an engineering firm logging service calls all need custom vocabulary tuning. Off-the-shelf transcription services may not offer it, or may charge per-call or monthly fees that become expensive fast. Before committing, ask the vendor whether they support custom vocabulary and at what cost.
Background noise in call centres is a real problem. If you operate a high-volume inbound call centre with open-plan seating, background chatter from other calls interferes with transcription quality. A 40-person operation with no sound dampening will see worse results than a small office with quiet equipment. This is not something better AI will fully solve. If noise is a factor, consider it a ceiling on accuracy from the start, not something to hope improves with better technology.
Regulatory compliance adds complexity that many standard transcription services do not handle. If you are bound by data privacy law, industry compliance rules, or contractual obligations to store call recordings in a specific way, the transcription vendor's infrastructure and certifications matter. Check their compliance documentation on their own site. Ask directly whether they can meet your requirements. If the answer is vague or you do not understand it, that is a reason not to buy.
How to Evaluate and Verify Capabilities Yourself
Start by checking the vendor's own public pages. Read the pricing page to understand what you actually pay for: per-minute costs, minimum commitments, overage charges, storage fees. Read the documentation to confirm which features exist and which do not. Check the security or trust page for certifications, data handling practices, and retention policies. If information is missing from those pages, you cannot assume the capability exists. Write down the gaps and bring them to a sales call.
Run a structured trial. Do not use the vendor's sample audio. Record 10-15 of your own recent calls. Transcribe them. For each one, read the output against a recording and count errors by category: missed words, wrong words, misattributed speakers, garbled sentences. Calculate your own error rate. Test on calls that represent your worst-case scenario: your noisiest environment, your most common accents, your technical jargon. Ask the vendor whether they will support custom vocabulary if you sign up, and whether that is included or extra.
Confirm storage and search in writing before you commit. Ask: where is audio and text stored geographically? How long is it retained? Can you download and delete it? Can you search across all transcripts, or only recent ones? If they say "we keep it as long as you need," that is not a written commitment. Get the actual retention period, the deletion process, and the search functionality in writing.
If you are using transcription to feed a CRM or phone system, confirm integration before signing. Some transcription vendors integrate with Salesforce or HubSpot. Some do not, or the integration is one-way only. Platforms with built-in CRM features often have tighter integration with transcription than standalone transcription vendors do. Confirm what data flows where, at what latency, and whether it is automated or manual. A trial that shows you an integration in a controlled environment does not prove it will work at scale on your actual calls.
Frequently Asked Questions
What is a reasonable accuracy target for call transcription?
It depends on your use case. For quick call notes in a CRM, 85-90% accuracy is often acceptable. For compliance recording or legal evidence, 95%+ is typical. For technical documentation or medical records, you may need 98%+. Test on your own audio to find your threshold, not on vendor benchmarks.
Does background noise always ruin transcription quality?
Not always, but it degrades it reliably. Modern systems are better than they were, but they cannot fully separate your agent's voice from office chatter. Acoustic treatment (sound panels, headsets with noise-cancelling) helps more than hoping better AI will fix it. Test in your actual environment, not a quiet demo room.
Can I use transcription as a legal record of a customer call?
Only if you understand the risks. Transcripts are not the same as recordings. Errors in transcription can misrepresent what was said. If the transcript is your only proof, you are at risk. Always keep the audio recording too. Confirm with your legal team whether transcription meets your compliance requirements before you rely on it.
How long should I keep call transcripts?
That depends on your industry and your contracts. Financial services may need to keep them for years. Customer service might keep them for months. Check your legal and regulatory obligations, then confirm the vendor can support your required retention period before you sign up.
What happens to my data if the vendor goes out of business?
You lose it, unless you have downloaded and stored it yourself. Ask in your contract what happens to your data in a business failure or acquisition. Get a data export process in writing. Do not assume you can always retrieve it.
If you want transcription as part of a larger system that includes call routing, CRM storage, and team collaboration, explore how voice AI agents with built-in transcription fit your workflow. Ready to see how call transcription works in practice? Book a call to discuss your specific use case and run a trial on your own audio.
Independent buyer's guide published by Sysevo. Sysevo is not affiliated with, endorsed by, or partnered with AssemblyAI, and AssemblyAI is the trademark of its owner. Product details change often, so confirm anything that matters to your decision with the vendor directly before you buy.
