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Introduction

Building a contact center application requires careful consideration of accuracy, speaker separation, compliance, and scalability. This guide addresses common questions and provides practical solutions for both post-call analytics and real-time agent assist scenarios.

Why AssemblyAI for contact centers?

AssemblyAI stands out as the premier choice for contact center applications with several key advantages:

Industry-leading accuracy on telephony audio

  • Universal-3.5 Pro model delivers best-in-class accuracy on 8kHz telephony audio
  • 2.9% speaker diarization error rate for precise agent vs. customer attribution
  • Multichannel support for stereo call recordings where agent and customer are on separate channels
  • Keyterms prompt allows providing call context to improve accuracy of company names, products, and compliance phrases

Streaming with Universal-3.5 Pro

For real-time agent assist, AssemblyAI’s Universal-3.5 Pro Streaming model (universal-3-5-pro) offers:
  • Low latency enables live transcription during calls
  • Format turns feature provides structured, readable output
  • Dynamic prompting via UpdateConfiguration to update context mid-call
  • Dual-channel streaming for separate agent and customer audio streams

End-to-end voice AI platform

Unlike fragmented solutions, AssemblyAI provides a unified API for:
  • Transcription with speaker diarization (agent vs. customer)
  • Multichannel audio support for stereo call recordings
  • PII redaction on both text and audio for HIPAA and PCI compliance
  • Post-processing workflows with custom prompting - from call summaries to QA scoring
  • Streaming and pre-recorded transcription in a single platform
  • Compliance and security built for enterprise workloads (BAA, SOC2, ISO)

When should I use pre-recorded vs streaming for contact centers?

Understanding when to use pre-recorded versus streaming is critical for contact center workflows.

Pre-recorded Speech-to-text

Post-call analytics - Call already happened, you have the full recording
  • Highest accuracy needed - Pre-recorded models have the highest accuracy
  • Speaker diarization is critical - Pre-recorded has 2.9% speaker error rate
  • Multichannel recordings - Most contact center recordings are stereo with agent and customer on separate channels
  • Compliance workflows - Full PII redaction with audio de-identification
  • Post-call analytics - Summarization, sentiment analysis, entity detection, QA scoring
  • Batch processing - Processing large volumes of call recordings
Best for: QA scoring, compliance monitoring, coaching insights, post-call CRM updates, searchable call archives

Streaming Speech-to-text

Live calls - Transcribing as the call happens You should use streaming when you need to display a live transcript to agents during calls. With Universal-3.5 Pro Streaming, accuracy is closer to pre-recorded, but pre-recorded will always be the most accurate option.
  • Agent assist - Live transcription visible to agents during calls
  • Real-time coaching - Prompt agents with suggested responses or compliance reminders
  • Live compliance monitoring - Detect compliance violations in real-time
  • No recording available - Processing live audio only
Best for: Agent assist, real-time coaching, live compliance monitoring, live call transcription Many contact center platforms use both:
  1. Streaming during the call - Provide live transcription for agent assist and real-time coaching
  2. Pre-recorded after the call - Generate high-quality transcript with speaker labels, summary, and analytics
Example workflow:
  • Call begins → Start streaming for live agent assist
  • Call ends → Upload recording to pre-recorded API for final transcript with speaker names
  • Generate call summary, QA score, and compliance report from pre-recorded transcript
  • Push results to CRM (e.g., Salesforce)

What languages and features for a contact center application?

Pre-recorded calls (Universal-3.5 Pro)

For post-call analytics, AssemblyAI supports: Languages:
  • 99 languages supported
  • Automatic Language Detection to route to the most spoken language
  • Code Switching to preserve changes in speech between languages
Core Features:
  • Speaker diarization (agent-customer separation)
  • Multichannel audio support - when agent and customer are on separate audio channels, enables perfect speaker separation without diarization
  • Automatic formatting, punctuation, and capitalization
  • Keyterms prompting for boosting domain-specific terms (up to 1000 terms for Universal-3.5 Pro)
  • Natural language prompting (Universal-3.5 Pro) - up to 1,500 words to guide transcription behavior
  • Speaker options with configurable min/max expected speakers for call transfers
Speech Understanding:
  • Summarization for call recaps
  • Sentiment analysis for customer satisfaction tracking
  • Entity detection for extracting names, account numbers, and products
  • Speaker identification to map generic labels to agent and customer names
  • Translation between 100+ languages
Guardrails:
  • PII redaction on text and audio for HIPAA and PCI compliance

Streaming (Universal-3.5 Pro Streaming)

For live call transcription, use Universal-3.5 Pro Streaming (universal-3-5-pro) for the highest streaming accuracy: Core Features:
  • Speaker diarization for identifying agent vs. customer
  • Partial and final transcripts for responsive UI
  • Format turns for structured, readable output
  • Keyterms prompt for company names, products, and compliance phrases
  • Dual-channel streaming for separate agent and customer audio
For more details, see the Universal-3.5 Pro Streaming documentation.

How can I get started building a post-call analytics pipeline?

Here’s a complete example implementing pre-recorded transcription for contact center call analysis:

How Do I Handle Multichannel Contact Center Audio?

Most contact center recordings are stereo with the agent on one channel and the customer on the other. Multichannel transcription gives you perfect speaker separation without diarization.

Pre-recorded Multichannel

When to use multichannel:
  • Call recordings from PBX systems with separate agent/customer channels
  • Recordings from platforms like Genesys, Twilio, Five9, NICE, or Talkdesk
  • Any stereo recording where each channel represents a different speaker
Benefits:
  • Perfect speaker separation - No diarization errors
  • No speaker confusion or overlap issues
  • Higher accuracy - Model processes clean single-speaker audio per channel

Streaming Multichannel

For real-time dual-channel transcription, create separate streaming sessions per channel:
See our multichannel streaming guide for complete implementation details.

How Can I Build a Real-Time Agent Assist?

Here’s a complete example for real-time streaming transcription optimized for contact center agent assist:

How Should I Handle Pre-recorded Transcription in Production?

For high-volume contact center workloads, use webhooks instead of polling:
Webhook handler example:

Scaling Considerations

  • HTTP rate limit: 20,000 requests per 5-minute window, counted across submissions (POST) and polling (GET) combined
  • Exceeding the limit: returns a 403 response
  • Parallel transcriptions (rate limit): 200+ for paid accounts (queued beyond that)
  • Ramp up gradually: start at 10-50 parallel requests, double incrementally
  • Avoid the rate limit: use webhooks or jittered, widened polling — see Polling without exceeding the rate limit
  • Contact Sales before large-scale rollouts

How Do I Handle PII and Compliance?

PII redaction is critical for contact center compliance (HIPAA, PCI-DSS, GDPR, CCPA).
Why hash substitution?
  • Stable across the file (same value = same token)
  • Maintains sentence structure for downstream LLM processing
  • Prevents reconstruction of original data

HIPAA Compliance

  • AssemblyAI provides a Business Associate Agreement (BAA) at no cost
  • Paid customers can review and sign our standard online BAA self-serve from the Data Controls page in the dashboard (Owner or Admin role required, upgraded account required)
  • Use PII redaction with audio de-identification for full compliance

How Do I Improve the Accuracy of My Contact Center Transcription?

Prompting Best Practices

The most impactful lever for contact center accuracy is prompting. Use a structured prompt with a Context: field:
Tips for effective prompting:
  • Use positive instructions (“transcribe verbatim”) not negative (“do NOT summarize”)
  • Start with fewer instructions, add one at a time — every added instruction risks conflicting with another. Treat the older “3–6 instructions” guidance as an upper bound, not a target.
  • Layer instructions one by one and test each against your call recordings to measure impact
  • Dynamize the Context: line per call with known info: company name, agent name, compliance phrases
  • Use keyterms for proper nouns and domain vocabulary (company names, product names, agent names)

Using Keyterms for Pre-recorded Transcription

Using Keyterms for Streaming

What Workflows Can I Build for My Contact Center Application?

Use these features to transform raw call transcripts into actionable insights.

Summarization

summarization: true What it does: Generates an abstractive recap of the call. Output: summary string (bullets/paragraph format). Great for: Post-call CRM updates, call recaps, supervisor review.

Sentiment Analysis

sentiment_analysis: true What it does: Scores per-utterance sentiment (positive / neutral / negative). Output: Array of { text, sentiment, confidence, start, end }. Great for: Customer satisfaction tracking, escalation detection, QA scoring.

Entity Detection

entity_detection: true What it does: Extracts named entities (people, organizations, locations, products, etc.). Output: Array of { entity_type, text, start, end }. Great for: CRM enrichment, auto-tagging topics, competitor tracking.

Speaker Identification

Map generic speaker labels to agent and customer names:

Translation

Translate call transcripts for international teams:

Redact PII Text and Audio

How Do I Process the Response from the API?

Processing Pre-recorded Responses

Additional Resources